DESCRIPTION: The project describes basic immunological and molecular biological studies of a lens-epithelium-derived growth factor (LEDGF), a protein possibly involved in the mechanism of age-related cataract (ARC), the leading cause of world blindness. In earlier publications, the PI showed that sera from patients with ARC contained antibodies (Abs) cytocidal for mouse and human lens epithelial cells (LECs) in culture. These cytocidal Abs were highly prevalent (96%) in patients with ARC. He began a search for the lens protein which could induce such a cytocidal Ab. From human LECs several clones were isolated using an auto-Ab probe from patients with ARC. One of these clones was isolated, purified, and its DNA sequence was determined. From this the amino acid sequence of LEDGF was deduced. LEDGF contains 530 amino acids and has a molecular weight was 61 kDa. A search of computerized data banks of primary protein structures revealed that LEDGF was highly homologous to hepatoma-derived growth factor. Its primary structure suggests that LEDGF may be a regulatory protein. LEDGF significantly stimulated the growth of LECs in culture. Anti-LEDGF Abs blocked this stimulatory effect, and cells incubated with anti-LEDGF Abs ultimately died. The seven specific objectives outline a plan to produce LEDGF, to define its secondary and tertiary structures, its tissue expression and its function in cell growth and differentiation. The PI will determine the amino acid sequence of its epitopic region and its antigenic potency to induce cytocidal anti-LEC Abs. He will isolate the LEDGF gene and produce a knockout mouse to further our assessment of the functions of LEDGF. In a mouse model he will define the age-dependency of LEDGF's effect on LECs. Also in a pilot clinical study the PI will recruit age- and sex-matched patients with clear lenses and ARC, do LOCs III-cataract classification, and anti-LEDGF Ab titers to determine the significance of any association with a particular class of ARC. The discovery of a lens-derived growth factor, an Ab which blocks its stimulatory effect, and the high prevalence of this Ab in patients with ARC comprise and immunological system which may modify the integrity of the lens epithelium, the metabolic "engine" of the lens, and cause age-related cataract.